Hippocratic oath
(The below is 95% a joke)
A story has been passed down in some parts of the world. It tells of a healer of some repute. On one day, a child comes to her with a crate in their hands. The child asks "Please, lady healer, my pet is sick and needs your help!" The healer looks inside the crate and sees a baby hippo in some distress. Not bothering to diagnose the malady, the healer grabs the first herb within reach and tells the child to feed it to the hippo once every morning for three days. The child thanks her and leaves.
Years later the healer is suffering from an affliction she cannot cure. She has heard of a new genius of medicine and visits to consult with them. "Please, o wise one, my bones weaken and my eyes blur. Have you any cure?" The genius looks at her a while, then stands up and returns bearing a crate. They open the crate to reveal a preserved set of bones. "Years ago you did not care enough to help my friend, and your negligence hastened his death. Why should I care for your plight now?" Now recognizing the child from years ago, the healer realizes the gravity of her sins. Prostrating herself, she proclaims "I vow to you here and now, that henceforth I will never abandon one in need of healing, nor shall I cause, through will or negligence, harm to one in my care." The genius provides her the knowledge to cure her affliction and many more secrets of medicine besides. The healer, now humbled, travels the land, using the genius' teachings to heal many and passing on the secrets to new generations of healers. To each new student she brings a crate containing preserved bones, and has them swear over the bones the oath she swore the genius.
This oath came to be known as the Oath Over the Hippo's Crate, but in time was corrupted into the Hippocratic Oath.